Minor bug fix; When skipping unknown slices, do not add a skip range of start==end==0! This causes the entire disk to compressed a second time!
Minor bug fix; When skipping unknown slices, do not add a skip range
of start==end==0! This causes the entire disk to compressed a second time!

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome